A locked machine gun includes locking parts on a breech mechanism and an abutment. These locking parts engage one another before the machine gun fires a shot. As will be readily appreciated, the locking parts are activated by the closing breech mechanism and, therefore, are abruptly subjected to stress. Additionally, the locking parts experience significant wear of tear because a machine gun may fire an extremely high number of rounds (at least some 105 rounds) during its life.
To account for this wear and tear, a conventional machine gun, such as the MG 42, uses an abutment that is coupled to a detachable barrel. When the barrel is worn out, it is scrapped along with the abutment. The movable locking parts that work with the abutment are associated with and coupled to the breech mechanism. Accordingly, these movable parts can be changed together with the breech mechanism and then, if necessary, be individually replaced in the armory.
Thus, the MG 42 has an advantage in that it is possible to change those wearing parts that are subjected to the most stress. On the other hand, a disadvantage is that the abutments are expensive to manufacture and they have to be changed in cases when only the barrel is worn out. Accordingly, there may be many instances in which the abutment is not worn out, but it must be replaced because the barrel of which the abutment is part is worn out. Further, abutment wear is not typically even.
The MG 42 is a recoil-operated gun with a removable barrel. With gas-operated machine guns, a gas piston facilitates the unlocking and loading motions, and the barrel remains rigid during the firing of a round. For this reason, the abutment in gas-operated machine guns is usually designed to be rigid in the casing of the weapon. Consequently, when replacing a worn abutment, the casing parts are also replaced.
Recoil-operated machine guns are also advantageous because it is easy to replace parts during use. If, for example, during the use of the weapon a quartz pebble falls into the abutment during the firing of a round, it is possible that the entire lock will no longer function. In the case of the recoil-operated MG 42, it is sufficient to change the barrel and if necessary the breech in order to make the MG fit for use again. The marksman can perform these activities on site in less than a minute. On the other hand, if a similar quartz pebble falls into the breech of a gas-operated MG, the weapon casing must be completely replaced. This cannot be performed in the field because the marksman of course does not carry a second weapons casing with him.
It is possible to assign the abutment to the barrel with the gas-operated MG, but the above mentioned disadvantages would still exist.